Writing a proper jUnit test

Question

over here I have made an assignment regarding a library system that I made in Java. I've had some negative comments about my written jUnit. My mentor told me that i'm not supposed to use if else statements in my unit tests. What would be the proper way to do it then? Because for what I think, I've been using this correctly.

Catalog.java

import java.util.ArrayList;

/**
 * The type Catalog.
 */
public class Catalog {

    private static ArrayList<Book> bookArrayList;

    /**
     * Instantiates a new Catalog.
     */
    public Catalog() {
        bookArrayList = new ArrayList<>();
    }

    /**
     * Gets book array list.
     *
     * @return the book array list
     */
    public static ArrayList<Book> getBookArrayList() {
        return bookArrayList;
    }

    /**
     * Sets book array list.
     *
     * @param bookArrayList the book array list
     */
    public static void setBookArrayList(ArrayList<Book> bookArrayList) {
        Catalog.bookArrayList = bookArrayList;
    }

    /**
     * Find book by title book.
     *
     * @param title the title
     * @return the book
     */
    public static Book findBookByTitle(String title) {
        for (Book book : bookArrayList) {
            if (book.getBookDetails().getTitle().equalsIgnoreCase(title))
                return book;
        }
        return null;
    }

    /**
     * Find book by isbn book.
     *
     * @param ISBN the isbn
     * @return the book
     */
    public static Book findBookByISBN(Long ISBN) {
        for (Book book : bookArrayList) {
            if (book.getISBN().equals(ISBN))
                return book;
        }
        return null;
    }

    /**
     * Loan book boolean.
     *
     * @param customer the customer
     * @param ISBN     the isbn
     * @return the boolean
     */
    public static boolean loanBook(Customer customer, Long ISBN) {
        for (Book book : bookArrayList) {
            if (book.getISBN().equals(ISBN)) {
                if (book.getAvailable()) {
                    book.setAvailable(false);
                    ArrayList<Book> b = customer.getRentedBooks();
                    b.add(book);
                    customer.setRentedBooks(b);
                    return true;
                } else return false;
            }
        }
        return false;
    }

    /**
     * Return book boolean.
     *
     * @param customer the customer
     * @param ISBN     the isbn
     * @return the boolean
     */
    public static boolean returnBook(Customer customer, Long ISBN) {
        for (Book book : bookArrayList) {
            if (book.getISBN().equals(ISBN)) {
                if (!book.getAvailable()) {
                    book.setAvailable(true);
                    ArrayList<Book> b = customer.getRentedBooks();
                    b.remove(book);
                    customer.setRentedBooks(b);
                    return true;
                } else return false;
            }
        }
        return false;
    }
}

CatalogTest.java

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import java.util.ArrayList;

class CatalogTest { //catalog Testing class
    static Customer customer1, customer2, customer3;    //all class 3 objects to store dummy data to test the methods
    static Book book1, book2, book3;
    static BookDetails bookDetails1, bookDetails2, bookDetails3;
    static Author author1, author2, author3;
    static ArrayList<Book> bookArrayList = new ArrayList<>();   //arrayList

    @Test
    void findBookByTitle() {   //testing method
        String bookName = "JavaBook1";  //finding JavaBook1 in book list
        Catalog.setBookArrayList(bookArrayList);    //set booklist in Catalog
        Book result = Catalog.findBookByTitle(bookName);    //find bookList
        if (result == null) {   //result null book not found
            Assertions.assertNull(result);
            System.out.println("Book not found!");
        } else {
            Assertions.assertEquals(bookName, result.getBookDetails().getTitle());  //book found
            System.out.println("Book Found");
        }
    }

    @Test
    void findBookByISBN() { //testingMethod
        long isbn = book1.getISBN();  //checking isbn
        Catalog.setBookArrayList(bookArrayList);    //setting arrayList into Catalog
        Book result = Catalog.findBookByISBN(isbn); //find book by isbn
        if (result == null) {   //result null book not found
            Assertions.assertNull(result);
            System.out.println("Book not found!");
        } else {    //else book found
            Assertions.assertEquals(isbn, result.getISBN());
            System.out.println("Book Found");
        }
    }

    @Test
    void loanBook() {   //loan books
        long isbn = book1.getISBN();    //get isbn
        long isbn2 = book2.getISBN();
        Catalog.setBookArrayList(bookArrayList);    //set booklist
        Assertions.assertTrue(Catalog.loanBook(customer1, isbn));   //loan book1 to customer
        Assertions.assertTrue(Catalog.loanBook(customer1, isbn2));  //loan book 2 to customer
        System.out.println("Total rented Books to customer 1  " + customer1.getRentedBooks().size());   //get size of loan books
    }

    @Test
    void returnBook() {
        long isbn = book1.getISBN();    //get isbn
        long isbn2 = book2.getISBN();
        Catalog.setBookArrayList(bookArrayList);    //set arrayList
        Catalog.loanBook(customer1, isbn2); //first loan books
        Catalog.loanBook(customer1, isbn);
        Assertions.assertTrue(Catalog.returnBook(customer1, isbn)); //test if book return fucntion work
        System.out.println("Book Returned");
        System.out.println("Total rented Books to customer 1  " + customer1.getRentedBooks().size());   //get size of loan books
    }

    @BeforeAll
    static void addDataForTest() {   //add Data for Test
        customer1 = new Customer("javaprogrammer1@email.com", "Java1", "73929474", "Netherland St:1", "1234", "Male", "cityNetherLand1", new ArrayList<>());
        customer2 = new Customer("javaprogrammer2@email.com", "Java2", "73929475", "Netherland St:2", "1235", "Male", "cityNetherLand2", new ArrayList<>());
        customer3 = new Customer("javaprogrammer3@email.com", "Java3", "73929476", "Netherland St:3", "1236", "Male", "cityNetherLand3", new ArrayList<>());
        author1 = new Author("author1@email.com", "Author1", "73926774", "Netherland1", "1237", "Male", "cityNetherLand1", 40);
        author2 = new Author("author2@email.com", "Author2", "73926775", "Netherland2", "1238", "Male", "cityNetherLand2", 50);
        author3 = new Author("author3@email.com", "Author3", "73926776", "Netherland3", "1239", "Male", "cityNetherLand3", 30);
        bookDetails1 = new BookDetails("JavaBook1", author1, 2019, "www.java1.com", "English", 400, "Netherland");
        bookDetails2 = new BookDetails("JavaBook2", author2, 2018, "www.java2.com", "English", 600, "Netherland");
        bookDetails3 = new BookDetails("JavaBook3", author3, 2010, "www.java3.com", "English", 500, "Netherland");
        book1 = new Book(Book.generateISBN(), bookDetails1, true);
        book2 = new Book(Book.generateISBN(), bookDetails2, true);
        book3 = new Book(Book.generateISBN(), bookDetails3, true);
        bookArrayList.add(book1);
        bookArrayList.add(book2);
        bookArrayList.add(book3);   //this Method is used for adding demo data to test Catalog Class Methods..
    }
}

Answer 1

I assume you want to test whether your find methods are finding the requested book. If a find method returns null, the test needs to immediately fail; there is no logic which should execute after that failure condition is encountered. This is why an if is not appropriate.

Think of assertions as meaning “stop immediately unless this condition is true”:

@Test
void findBookByTitle() {   //testing method
    String bookName = "JavaBook1";  //finding JavaBook1 in book list
    Catalog.setBookArrayList(bookArrayList);    //set booklist in Catalog
    Book result = Catalog.findBookByTitle(bookName);    //find bookList

    Assertions.assertNotNull(result,
        "Failed to find a Book with the title \"" + bookName + "\".");

    Assertions.assertEquals(bookName, result.getBookDetails().getTitle(),
        "Returned book does not have the correct title.");
}